Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
144 AM EST Thu Nov 14 2019
Valid 12Z Sun Nov 17 2019 - 12Z Thu Nov 21 2019
...Pattern Overview and Guidance/Predictability Assessment...
Upper pattern will transition toward western troughing and eastern
quasi-zonal flow in about a week after two successive systems lift
northeastward along the East Coast. In the West, upper ridging
will weaken on Monday as it slides eastward atop a closed upper
low moving westward away from Baja California. This will pave the
way for a Pacific shortwave to dig through interior California as
downstream heights rise in response toward the Ohio Valley.
Off the Southeast coast, the models have come into better
agreement with a lead surface low offshore Sun-Mon. Kicker trough
through the lower MS Valley showed more spread among the guidance
with the UKMET/Canadian quicker than the GFS/ECMWF and most of the
ensembles. Preferred the GFS/ECMWF-led consensus which was closer
to continuity. That kicker trough will likely spin up another sfc
low off the coast that will lift northeastward and possibly
develop in earnest off or near New England, depending on northern
stream flow across the Great Lakes. GFS runs were deeper and
closer to the coast than the ECMWF and the ensemble means. Given
inconsistency in shortwave timing the past several days, preferred
to keep the system outside the 40/70 benchmark next Wed.
In the West, the leading front into Washington on Sunday will
weaken in favor of a stronger shortwave on its heels. The ECMWF
continued to be more aggressive than the GFS and has wobbled
farther south or north with each run. Trend does seem to give
merit toward a stronger shortwave or possibly closed low. To the
south, the closed low off Baja California may eventually get
tugged back to the coast given enough digging of the incoming
trough Tue/Wed through the West. This would act to lower heights
over the Southwest via interaction/merging of the two features.
Confidence is low in details due to timing uncertainties.
Overall, a GFS/ECMWF/GEFS/ECMWF ensemble mean blend sufficed
through much of the period. Trended increasingly toward the
ensemble means due to their more modest depictions of the western
troughing and exiting eastern system next week.
...Weather Highlights/Threats...
Below average temperatures in the East on Sunday will slowly
moderate back toward more typical mid-November values by Tuesday.
Much of the West will have temperatures above normal by 5-15
degrees Sun-Tue before troughing brings in cooler temperatures
within about 5 degrees of average.
The lead system off the Mid-Atlantic coast should keep the
heaviest rains offshore but could be close enough to produce some
showers right along the coast. The strong pressure gradient
between the low and the sfc high exiting New England will lead to
windy conditions along the coast and especially over the nearshore
waters. Please see the Ocean Prediction Center's products for more
information. Second area of low pressure may bring rainfall
farther west, depending on the track. Per the forecast, the
precipitation shield will move northward into New England late Tue
into Wed where temperatures may be cold enough for some snow in
higher elevations Wed-Thu.
Several systems out of the Pacific will maintain a rather wet
period for at least coastal Washington/Oregon and the Cascades
Sun-Wed. Lighter rain/snow along is forecast for areas along the
Continental Divide and even lighter amounts into the High Plains.
With increased troughing toward the Southwest next week,
precipitation chances will increase Wed into Thu. Some rain is
possible for the lower/coastal elevations of southern California
into some of the deserts with higher amounts in the terrain.
Fracasso
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:
https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml